(a) Field of the Invention
The present invention relates to a corneum puncture needle used in a device for measuring chemical components contained in effusion or exuded body fluid from human tissue, and more particularly to the structure of a puncture needle used in a corneum puncture device for obtaining tissue fluid from under the skin corneum.
(b) Description of the Related Art
Measurement of chemical components in the human body such as glucose and lactic acid is medically important. Conventionally, such measurement has mainly been carried out through measurement of components in collected blood. The concentration of each component is measured through, for example, observed changes in color and light absorption of test paper, or detection of an electrical signal from a biosensor that converts the concentration into an electrical signal. Blood collection is usually carried out by use of a collecting needle, which is caused to puncture a vein or blood vessel in an arm of a human body. However, such puncturing involves the examinee experiencing physical pain and apprehension.
Recent improvements in measurement apparatuses enable the components in the human body to be measured using a sample of as small as a few microliters. Accordingly, there has been developed a method for collecting blood in which a thin collecting needle having a diameter of a few tens of micrometers is inserted into a blood capillary in order to collect blood. An example of such a method is described in, for example, Patent Publication No. JP-A-95-132119. However, there is a disadvantage in the blood collecting device described in this publication in that the hollow needle made from a silicon nitride film having a thickness on the order of 1 micrometer (xcexcm) is very brittle. In this respect, there exists the possibility that the needle is bent in the course of puncturing the skin, resulting in closure of the through-hole of the needle, as well as the possibility of the needle breaking off to be left in the body. Further, since blood contains red cells having a diameter as large as 10-20 xcexcm, when the red cells are passed through a thin tube having a diameter of a few tens of micrometers, hematolysis (rupturing of red cells) occurs, with the result that the concentrations of chemical substances in blood change.
Meanwhile, there has been developed another method in which, in place of conventionally used blood, effusion or exuded fluid collected from the skin surface is used in order to measure components within the human body. This method is reported in, for example, Proc. of the First Pan Pacific Symposium, Vancouver, Canada, July, 57-58, 1986, and Proc. of the 35th Meeting of Japan Society of Medical Electronics and Biological Engineering, 474, 1996.
Effusion is a small amount of fluid obtained through depressurization and suction of a portion of a skin surface from which the corneum has been removed, and is considered to be interstitial fluid or fluid effused from the wall of a capillary vessel by means of filtration under reduced pressure. Since effusion is lower in protein concentration compared to blood, in a measurement using a sensor, only a small amount of protein adheres to the surface of the sensor, resulting in increase of the service life of the sensor. Further, since effusion is collected through the skin, use of effusion is advantageous over collection of blood, in terms of reduction of pain imparted to the examinee and prevention of infection with pathogenic bacteria. This method is described in Patent Publication Nos. JP-A-92-341241, JP-A-97-51878, JP-A-97-140687.
In the method described in JP-A-92-341241, the corneum at a portion of the skin from which effusion is to be collected is first removed through use of an adhesive tape (hereinafter referred to as a xe2x80x9ctape stripping methodxe2x80x9d), and effusion is then obtained through depressurization and suction. However, the removal of the corneum by the tape stripping method involves the following problems.
A first problem is that the removal of the corneum by the tape stripping method requires considerable skill. Corneum thickness and the degree of ease in removing the corneum vary with location on the human body, the age and sex of the examinee, and the like. When removal of the corneum is insufficient, effusion cannot be collected. On the other hand, when removal of the corneum is excessive, bleeding occurs with resultant pain. Therefore, a considerable level of skill is required for removing the corneum to a degree that enables collection of effusion without causing bleeding.
A second problem is that even a skilled person requires 30 minutes or more to remove the corneum by the tape stripping method. During this period, the examinee must be motionless.
A third problem is that a portion of the skin from which the corneum has been removed requires about two weeks for regeneration.
A fourth problem is that in the tape stripping method, since adhesive tape does not contact uniformly with the skin, the corneum is difficult to remove uniformly, possibly resulting in decreased efficiency in collecting effusion.
The problems involved in the method described in JP-A-92-341241 can be solved through employment of the method described in JP-A-97-51878, in which the skin surface is punctured and the punctured portion is suctioned to collect effusion. However, the puncturing/suction device described in JP-A-97-51878 has a problem in that a puncturing needle does not effectively penetrate through the corneum, due to the uneven structure of the skin surface and deformation of the skin upon receipt of puncturing pressure. Simply increasing the length of the puncturing needle and puncturing pressure increases the degree of invasion into the skin, however, without effective collection of effusion.
JP-A-97-140687 describes a method of suctioning and collecting effusion through direct insertion of a hollow needle into the skin, whereas JP-A-97-510879 originated from an International Application describes a method of collecting interstitial fluid by use of a medical needle or the like. However, in order to insert a needle into the skin, these methods require a complicated apparatus for controlling the puncturing pressure and puncturing depth of the needle. Therefore, these methods involve the problem of employing expensive apparatus, as well as the problem of difficulty in collecting effusion. Further, the method of collecting effusion by use of a hollow needle involves the problem that effusion cannot be collected efficiently, due to viscosity of effusion.
It is therefore an object of the present invention to provide a corneum puncture needle capable of effectively collecting effusion substantially without deformation of skin surface and damaging blood vessel.
The present invention provides corneum puncture needle including a needle body and a stylus extending from the needle body to be inserted into a corneum of a human body, the stylus and the needle body forming therebetween a stepped portion acting as a stopper when the stylus is inserted into a corneum of a human body.
In accordance with the corneum puncture needle of the present invention, the stepped portion functions as a stopper, which enables the stylus to penetrate the corneum without damaging vein or blood vessel while preventing the skin surface from deformation. Thus, effusion can be collected with ease.